The present invention generally relates to a driving method of a display apparatus for AC driving display materials such as liquid display and so on to effect the picture display by the use of active matrixes formed with switching elements and picture element electrodes of thin film transistors (hereinafter referred to as TFTs) and so on in a matrix shape. The present invention has for its object to provide a driving method of the display apparatus, which comprises the steps for reducing the driving power, improving the display picture quality, improving the driving reliability, and improving the brightness thereof.
Generally, the display quality of the active matrix liquid display apparatus has been greatly improved in recent years, and reaches the equivalent to that of a cathode-ray tube (CRT). When the TFT array which ensures the best picture quality in the liquid crystal display apparatus is used, a DC voltage which is inevitably generated by the parasitic capacity and so on of the display apparatus interior is generated. The difference .DELTA.V between the electric potential Vt of the opposite electrode for AC driving the liquid crystal and the average central electric potential Vsc of the picture signal voltage is as follows in the case of no storage capacity: EQU .DELTA.V1=Vsc-Vt=CgdVg/(Clc+Csd),
wherein the storage capacity of the display unit, the liquid crystal capacity, the capacity between the source and drain are respectively Cs, Clc, Csd in the display unit shown in FIG. 1, namely, the electrical potential change of the scanning signal of the TFT is defined as Vg.
Also, in the case of the existing storage capacity, the difference .DELTA.V is defined as follows: EQU .DELTA.V2=Vsc-Vt=CgdVg/(Cs+Clc+Csd)
Namely, .DELTA.V1&gt;.DELTA.V2.
The DC electrical potential difference .DELTA.V gave applied influences upon the picture characteristics such as flicker of the picture image, sticking effect which is a memory of the picture image, stability with respect to the temperature, and so on. Especially when the storage capacity does not exist, the DC electrical potential difference becomes conspicuous. In order to remove the above described influences, the storage capacity becomes indispensable. Accordingly, the storage capacity is essential for eliminating the above mentioned bad influences, and at present a method for forming the storage capacity on the TFT array basic substrate may have the following case.
1) In a method of making electrode of the storage capacity with transparent electrodes, the construction and step of TFT arrays are complicated although the driving is simple, the area of the transparent electrode is large, and the bright display is provided.
2) It is made of metal of the gate electrode instead of the storage capacity electrode of the transparent electrode of the method 1). Although the construction of the array of TFTs is simple, with the driving method similar to the method 1) being possible, the area of the transparent picture element electrode becomes smaller, with a disadvantage that the open area ratio is smaller, thus resulting in the dark display apparatus.
3) The other method is to have the gate electrode and the electrode of the storage capacity in common use. Although as the characteristics, this method is simple in the step and the open area ratio becomes large, the large signal voltage is necessary, and the driving method of more consumption power is required.
In the known liquid crystal display apparatus using the TFT array with the storage capacity being built in, there has been no method of simultaneously satisfying the demands of more light, less flicker, with the construction being simpler and the consumption power being less. The TFT array of the method 3) among the above three methods may provide a liquid crystal display apparatus which is simple in construction and is large in the open area ratio, so that the development of driving method of for providing especially with the proper low consumption power has been desired.
According to the report of K. Suzuki: Euro Display 87 P107 (1987), there is a proposal of a method for employing a negative additional signal (Ve) to be applied after the scanning signal so as to completely compensate for the above described difference .DELTA.V. But, in this method the picture signal voltage is large, so that the driving is not effected with the lower consumption power.
On the other hand, the present inventors have proposed a driving method of satisfying the above described demands at the same time in Japanese Patent Application Serial. Nos. 63-58465, and 63-313456. Namely, with this method, firstly, the output signal voltage of the signal driving circuit in the active matrix display apparatus is considerably reduced, thereby reducing the consumption power of the signal driving circuit handling analog signals. Secondly, the display picture quality is improved, and even in the AC driving for each field, the causes of generating the flicker is improved. Thirdly, the reliability of the display apparatus is improved. This is because the DC voltage which has been inevitably generated within the display apparatus is removed by the capacity coupling and so on through Cgd of the anisotropy . scanning signal of the liquid crystal. By the removing of the DC voltage, the image sticking effect phenomenon of the picture to be caused immediately after the fixed picture has been displayed is considerably improved.
However in the above described driving method, the picture signals which are the analog signals become less, but the scanning signals are complicated enough to require the more power supply, with a disadvantage that IC chips become bigger, and the consumption power on the scanning side increases.